1. Technical Field of the Invention
This invention most generally relates to the application of paints and other materials by spraying from a spray gun configured with a top mount feed cup, and in particular, it relates to a top mount feed cup with a pressure proof gasket plate and adapter fitting.
2. Background Art
The art of spray painting of paints and other liquid materials using a handheld spray gun with a nozzle from which the liquid material is emitted in a stream or an atomized spray directed towards the target, is well established. A relatively low viscosity fluid mixture of desired material is most often supplied through the gun to the nozzle from a remote container and hose, or a feed cup attached to the underside or top side of the spray gun body. Depending on the system, the fluid may be supplied through the gun body to nozzle by gravity feed, siphoning or pumping action, or by pressure applied to the liquid reservoir to push the liquid into the gun.
Top feed cups are used in both pressurized and non-pressurized systems. The cups and lids, which are typically fabricated of plastic or metal, must be impervious to the methylene chloride and other active ingredients in the paint strippers and solvents that are used for cleaning and maintaining this type of equipment.
The top feed cups of hand held spray guns typically have a funnel-shaped bottom with a threaded nipple for screw-on attachment to the barrel of the gun. Exterior threads at the top of the cup wall accept a full diameter threaded dome cap or lid with a vent, pressure inlet, or check valve in the center. In use, the lid is screwed onto the filled cup, contacting and rotating along the top edge of the cup until increasing turning torque suggested a compressive seal has been attained. The check valve, where used, permits ingress of air but closes under pressure, as is needed for the on/off application of drive air in a turbine powered high volume, low pressure (HVLP) system or for retaining the pressure in a conversion gun. A simple, non-spill vent is used in gravity feed and suction systems.
Bottom feed cups have only a top opening, through which support, and access for filling and cleaning, as well as feed tube and venting or pressure is accomplished. The attachment fitting for a bottom feed cup is necessarily larger than for a top feed cup, due to the added size needed for filling and access.
The lid to cup seal in the typical, top cup, screw-on lid arrangement, is subjected to rotational contact and frictional wear while being compressed, contributing to poor sealing and deterioration of the seal surfaces. Elevated air pressure in the pressure cups of the prior art exerts a deforming stress on the sidewalls of the cup and on the entire inner surface area of the lid. The stress and related deformation tends to open the seal joint by leverage and distortion of the thread interface. The gun and cup are subjected to constant motion in use, and the reactive movement of the cup""s contents assures that the liquid contacts the full circumference of the cup/lid juncture and inevitably works into any area along the perimeter that may be susceptible to leaking.
In fact, most top feed paint spray gun cups, both pressurized and non-pressurized, are notorious for leaking around the cap or lid, resulting in a mess on the operator""s gun, hands, and often on the object being painted. There seems not to be any simple, lightweight, inexpensive means of reliably sealing these cups, particularly for pressurized systems where pressure is applied to the paint cup.
One prior art offering, directed at the leakage problem, xe2x80x9c . . . designed either for gravity paint feed or, preferably, for suction feed in combination with gravity feed.xe2x80x9d (Col. 2, line 28), is disclosed in Kosmyna et al""s U.S. Pat. No. 5,582,350; a hand held paint spray gun with top mounted paint cup. Here, the cup is configured with a tapered top edge rim, and with external locking knobs on the cup wall below the taper. The cup lid is configured with a V-groove that fits over the tapered edge of the cup rim, and a locking ring with external bayonet type structures that engage the locking knobs by partial rotation of the locking ring, to seal the lid to the cup.
This arrangement suggests, although does not explicitly recite, a non-rotating seal engagement, where the lock ring is rotable relative to the lid, eliminating the rotational friction at the seal between the cup and lid while the lid is being locked in place. However, this design was expressly intended for other than pressurized systems, and does not speak to or anticipate the problems that pressure introduces to the design. It also does not suggest a kit methodology for modifying or retrofitting an existing paint cup and lid assembly to obtain the alleged benefit of the design.
In summary, problems heretofore exhibited in the art of spray guns includes pressurized paint spray guns with top feed cup and lid assemblies that are unreliable in retaining paint without leaking during the course of the work.
The invention in its simplest form is a locking lid and floating gasket plate assembly for pressurized, top cup spray guns such as are commonly used for spraying small quantities of paint, and other fluids. In this form, the invention assumes a conventional top cup with external threads at the top of the cup wall for rotationally advancing attachment of a lid. At the core of the invention is a relatively stiff, flat, rigid, pressure proof, gasket plate intended to be secured to the top of the cup with a special lid. The domed lid here functions as an edge lock structure on the gasket plate, that is separate and distinct from the gasket plate, so as to be rotable as to the plate, and isolated from cup pressure so as to be not susceptible to deformation from cup pressure. The lid further functions as a full splatter shield, with a closely conforming center clearance hole for an adapter fitting in the gasket plate.
A vent, pressure feed or check valve fitting, according to the type of system in which the cup is employed, is connectable to the center mounted adapter fitting. The adapter fitting protrudes or is accessed through the closely fitting co-axial opening in the lid. The gasket plate is fabricated of flat stock for economy and simplicity of design, and forms a relatively rigid top to the pressure chamber within the cup. The adapter fitting in the plate replaces the fitting normally found mounted in the lid.
The floating gasket plate is slightly larger than the diameter of the cup rim. When the lid is screwed down on or otherwise compressively attached to the top of the cup with the gasket plate in between, the gasket plate forms a stationary, compressive, full ring seal on the cup rim and a pressure proof top to the paint cup. The gasket plate is designed and constructed of material sufficiently strong to contain the working pressure within the cup without deforming significantly, which aids in maintaining the integrity of the seal. The gasket plate is compressed at its periphery by the outer edge of the inside surface of the domed lid against the top edge of the cup as the lid is screwed onto the cup. There is no contact between the plate and the lid except at their peripheries. The lid is thereafter susceptible only to unidirectional lifting force vectors, and not to the stress and deformation caused by pressure across its entire surface.
The plate to cup seal is unaffected by rotational friction and distortion as the compression is applied, and is thus free of small or microscopic damage and wear caused by the rotating compressive engagement. The lid and the cup and lid threads are likewise isolated from contact with the materials being sprayed.
The significantly improved leakage characteristics of the invention permit the use of a double ended paint can similar to the top feed embodiments, to be used upside down for bottom feeding of the spray gun, where the gun and/or the attachment fixtures are suitably modified.
It is therefore an object of the invention to provide a leak proof paint cup assembly or kit for retrofitting an existing paint cup assembly, for use with a top feed spray gun.
It is a further object to provide a practical feed cup with a bottom side opening for filling and cleaning, for use with a bottom feed spray gun.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein I have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by me on carrying out my invention.